apache/druid · error · RejectedExecutionException

Service is not started.

Error message

Service is not started.

What it means

HttpPostEmitter.awaitStarted() waits up to 1 second for the emitter's start latch. If the emitter was never started (or hasn't started within 1s), emit/flush attempts throw RejectedExecutionException 'Service is not started.' This prevents silently queuing events into an emitter that will never send them.

Solutions

1. Call emitter.start() before emitting or flushing any events
2. Ensure startup isn't delayed beyond 1 second (check the EmittingThread for blocking initialization)
3. Check for a prior close/termination that stopped the service; create a fresh emitter if needed
4. Catch RejectedExecutionException around emit/flush to detect lifecycle misuse and requeue or log

Example fix

// before
HttpPostEmitter emitter = new HttpPostEmitter(config, mapper);
emitter.emit(event); // RejectedExecutionException
// after
HttpPostEmitter emitter = new HttpPostEmitter(config, mapper);
emitter.start();
emitter.emit(event);

if (!emitter.isStarted()) {
  emitter.start(); // or await startup before emitting
}

try {
  emitter.emit(event);
} catch (RejectedExecutionException e) {
  log.warn("Emitter not started; starting and re-emitting");
  emitter.start();
  emitter.emit(event);
}

When it happens

Trigger: Calling emit(), flush() (via emitAndReturnBatch/flush -> awaitStarted) on an HttpPostEmitter before start() was called, or when start() has not completed within the 1-second await window.

Common situations: Forgetting lifecycle start in embedded usage; emitting immediately after construction; a blocked or slow startup thread exceeding the 1s latch timeout; emitter created but start() skipped in tests.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• Already started.
• Already started, not starting again
• can't stop.
• Could not start lifecycle
• Dictionary not serialized, cannot open value serializer

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/5dac0d5ba285835c. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/java/util/emitter/core/HttpPostEmitter.java:205

  public void start()
  {
    synchronized (startLock) {
      if (!running) {
        if (startLatch.getCount() == 0) {
          throw new IllegalStateException("Already started.");
        }
        running = true;
        startLatch.countDown();
        emittingThread.start();
      }
    }
  }

  private void awaitStarted()
  {
    try {
      if (!startLatch.await(1, TimeUnit.SECONDS)) {
        throw new RejectedExecutionException("Service is not started.");
      }
      if (isTerminated()) {
        throw new RejectedExecutionException("Service is closed.");
      }
    }
    catch (InterruptedException e) {
      log.debug("Interrupted waiting for start");
      Thread.currentThread().interrupt();
      throw new RuntimeException(e);
    }
  }

  private boolean isTerminated()
  {
    return concurrentBatch.get() == null;
  }

  @Override

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